High power lasers provide beams of coherent radiation characterized by high beam quality. Preferably, the laser output of a high power laser is characterized by a uniform wavefront. Because they produce high power, coherent radiation, high power laser systems have been used in a wide variety of applications. Industrial applications for high power lasers include laser cutting and welding, laser marking, and the like. In many applications, one of the metrics of interest is the beam intensity, measured in power per area (W/m2) at a focal point. A beam with a uniform wavefront will ideally focus to a diffraction limited spot size. However, as laser beams propagate through laser optics, which are nearly always imperfect, scattering from small-scale obscurations and phase objects cause high-spatial-frequency variations in intensity and wavefront across the beam. Such intensity variations increase risk for optical damage to laser optics, and both intensity variations and wavefront variations increase the laser spot size for subsequently focused laser beams, thereby decreasing the beam intensity. For applications dependent on high beam intensity, this condition is undesirable.
In order to improve beam quality, pinholes have been utilized to spatially filter the laser beam, removing high-spatial-frequency wavefront and intensity variations. Typically, a laser beam is focused using a lens and a pinhole is placed in the focal plane, spatially removing aberrated rays at positions blocked by the pinhole. A second lens is then used to collimate the laser beam, providing a beam with a more uniform intensity and more uniform wavefront suitable for high intensity applications.
Despite the benefits in beam quality provided by pinhole spatial filters, several problems are presented by the use of pinhole filters. Thus, there is a need in the art for improved methods and systems related to spatial filters for high power lasers.